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A. R. GOODWIN. VARIABLE GRID` RESISTANCE. APPLICATION FILED SEPT. 8,i921.

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AUBREY R.. G-OODWN, O1? MELROSE, MASSAGI'ISETTS, A'SSIGNOB, TO CHELSEARADIO oo., or CHELSEA, rrassnorrusnrrs, .araiarlvnrtsrirr coNsrs'rrNG-eoonwlru, VOamaru-iroa'rntno, AND PELLEGRINO Rizzo.

0F AUBREY R.

VARIABLE GRU) RESISTANCE.

Macnee.

Specification of Letters Patent.

Eat-rented June 20, 1922.

Application filed September 8, V1921. i Serial No. 499,173.

To all w/wmfz't may concert.'

.Be it known'th'a't AUBREY R. GOODWIN, a citizen of thefU'nited States,residing at Melrose, in the county of Middlesex and Stater ofMassachusetts, have invented new and useful Improvements in VariableGrid Resistances, of'f'which the following isA a specification. 'l

This invention -relates to a variable grid resistance-" In radiocommunication a device known as a vacuumftube7 'is' universally `used toreceive, amplify and generate oscillations.,

This vacuum tube consists of an evacuated glass bulb containing threeelements known as the :[ilament, grid and plate;

Metallic'bodies when heated to a dull red glow, or higher temperature,throw olf negative electrons. When'both the plate and grid are at zeropotential thesev nega` tive electrons are propagated by the filament inall directions. If, however, the plate becomes positively electrifiedthe negative electrons are attracted to it and electrified, it repelsthe'negative electrons,V reducing the valueof the. electron stream, andif the grid becomes` suiiiciently charged` to a negative potential, itmay stop the flowy of electrons to the plate altogether.

In radio communication, the circuits are' so arranged that the incomingoscillations from the antenna act upon the grid, which alternatelybecomes positively and negatively charged. During the positive charge,however, all of the negative electrons are not removed from the grid,hence the grid during Vthe many succeeding oscillations accumulates anegative charge which is not removed during the'positive half of thecycle and materially reduces the flow of the electron stream and itbecomesV necessary to use some auXiliaryvmeans to,v remove this eX-cess'negative potential and hence the use of the grid resistance, whichifof the proper value allows the eXtra negative charge of the grid toleak off and keeps the vacuum tube in its most sensitive operatingcondition.

The amount of thisy negative accumulation on the grid varies with theincandes- 'cence of the filament, the positive potential on the plate,the degree of evacuation of the tube and the gas content of the tube.VIf the tube contains a considerable amount of gas, part lof the excessnegative charge on the grid will leak to the filament through the gasitself. ln very highly evacuated tubes no such 'leakage can take placeand a grid resistance mustbe employed. To meet these changing conditionsin a tube and the differentcharacteristics of different tubes, a fixedvalue of grid resistance is insuflicient to maintain the tube at itsproper operating characteristic, and hencek I have devised a variablegrid resistance, which allows the introduction of the proper leakresistance at will, and hence an immediate and accurate control of thegrid potential and the means for always maintaining the vacuum tube atits proper operating characteristic.`

The object of the invention is to provide a device'by'means of'which avacuum tube may always 'be kept' at its most sensitive operatingcondition. i

The invention 'consists in the combination and arrangement of parts setforth in the of a device any suitable insulating material, but prefer-`ably of material which may be moulded as desired. A recess 6 is formedin the rear side of the base 5. Centrally located upon the base 5 is aswitch 7 embodying therein, a contact arm 8 constructed of resilientsheet metal, an Aoperating handle 9 constructed of insulating materialand a stud 10 which constitutes a pivot for the switch 7 and'is securedtoY the operating handle 9 by a screw ll in such manner as to also clampthe contact arm 8 between a shoulder 12 provided upon the stud 10 andthe operating' handle, whereby said operatinghandle, stud and contactarm may be rotated in unison. The stud 10 is electrically connected bymeans ot a strip o'l sheet metal 13 located within the recess G with asuitable binding post 14: to which an electric wire 15 may be attachedin the usual well-known manner.' The stud 10 projects slightly throughan openingl 1G provided in the strip l5 and the latter springs intocontact with a washer 17 secured at the end ot' the stud l0 by a screw18.

Mounted upon theV base 5 and. arranged concentric with the median 4aXialline oit the switch 47 are a plurality ofstuds 19 constitutingcontacting points. The studs 19 are shouldered at 2O and project intoopenings 2 1 provided in the base 5, being clamped to said base byscrews 22. `Loc-ated within the recess and clamped against the undersurface of the base 51h-y means of the screws 22 is apiece Qt sheetmaterial Q3, upon a portion oit the surface o'l which is a deposit otdried ink 24 which extends in an arc parallel with thecenter line ot thecontact studs 19. The sheet material 2S is a non-conductor forelectricity. `From the curved ink surface 24 radial branches 25 extendbeneath each of the screws 22 with the exception oit a. sere-w 22Elwhich has no connection with the ink surface. The ink surface is aconductor :tor an electric current and constitutes a resistance throughwhich the extra negative charge ot a vgrid previously mentioned mayleak.

The ink surface 24 is electrically7 connected topa strip of sheet metalQ6, one end of which in secured beneath a screw 22h and connects `withasuitable bindingpost 27 to which `an electric wire 28 may be attachedin theusual well-known manner.

Stop pins 29 and 30 are suitably positioned upon lthe upper surtace otthe base 5 in the kpath oflythe contact arm 8 and limit the movement oitsaid arm in either direction. Numerals trom O to 9vare placed upon theouter surface of the casing,- 5 adjacent to the Contact studs 9 andrepresent'. ditlercnt values ot' grid resistance trom one-halt' mil lionohms to tive million ohms in steps o'E lapppronnnately one-half millionohms. The

contact stud which is not connected with the resistance material 24 andwhich is indicated at 19a is secured in thebase 5 by the screw 22a. Thisstud 19l which is not included in any electric circuit through thedevice has.' a numeral 10 located upon the upper surface of the casing 5adjacent thereto.

In practice the device illustrated may be connectedy by a shunt tothegrid condenser, or as is usually the case, between the gridandtheiilamcnt. The switch 7 is rotated by means of the operating'handle 9 to locate thearm S in contact with the stud 1.9 which is foundwill lzeep the vacuum tube in its most sensitive operating? condition.hlany vacuum tubes 'will not function without the aid ot a `"ridresistance and the elliciency o'l operation is greatly increased by theuse ot a, variable resistance.

Although nine di'tlerent values ot resistance are obtainable with thedevice illustrated in the drawings, either a smaller or larger numbermay be used without departingtrom the spirit of this invention.

It is also evident thatwhili-x a circular instrument base is illustratedinthe drawings, any form of base may be employed and the contact studswhich are illustrated positioned in an arc concentric withthe medianline of the switch may be arranged in a straight line, or otherarrangements adaptable to the best operation of the type of switchemployed.

The device herewith illustrated and described may be employed in radiocommunication in connection with transmitting vacuum tubes as well asreceiving tubes and irrespective ot their Functions, whether asdetectors, amplifiers or oscillators.

I claim:

1. In combination, a leal( resistance material and a switch constructedand arranged to co-operate with said resistance material to produce aplurality ot predetermined. values of leak resistance.

2. A. device ot' the character described having', in combination, a baseconstructed of insulating` material, a lealrresistance ma terial securedto said base, a. plurality of electric Contact points communicating withsaid lea-lr resistance material and a switch constructed and arranged toengage said contact points.

8. A device ol the character described. having, in combination, acircular moulded base ot insulating material, a lealr resistancematerial secured to said base, a plurality of studs 'fast in said haseand arranged in an are concentric with the center ot said hase, saidstuds con'iniun'icatiug with said. leali resistance material and aswitch eonstructed and arranged to engage said studs.

4f. A device oill the character described having, in combination, a baseconstructed. of insulating, material, a layer ot' insulatingr materialfast to said base, a deposit ot leal; resistance material upon saidinsulating material, a plurality of contact studs 'fast in said base andcommunicating with said leak resistance material and a switchconstructed and arranged to engage said contact studs.

5. A. device of the character described having, in combination, a. baseconstructed of insulating material, a layer ot insulating material tastto said base, a deposit ot dried ink upon said insulating` material, aplurality ot contact studs 'tast to said base and communicating withsaid ink deposit and a switch constructed and arranged to engageconstructed and arranged to engage said said contact studs. contactstuds to produce a plurality of pre- 6. A device of the characterdescribed determined values of leak resistance. having, in combination,a base constructed In testimony whereof l have hereunto set 15 5 ofinsulating material, a layer of insulating my hand in presence off twosubscribing Witmaterial fast to said base, a deposit of dried nesses.ink upon said insulatingmaterial, said ink deposit having branchesextending there- AUBREY R GOODVIN' from7 a plurality of Contact studsfast in Witnesses: 10 said base and communicating with the FRANKLIN E.LOW,

branches of Said ink deposit, and a switch KATHRYN M. JOYCE.

